An idea for itemisation into shielding champions.

Teams have the most trouble with shields late game, shielding a kog'maw 3 times is a really nasty and effective strategy to put a clock on the enemy time, beat us before we can set up a mobile turret that aces your team. Shields help in one way: they give you a lot of hp in anticipation of incoming damage.

This can then allow you to go on the offensive: when you don't have to move from a certain amount of incoming damage, you get to have uptime on your damage and uptime on a hypercarry can mean a won team fight in less than seconds. Getting a good flank off, or getting a great engage can actually be a mistake into a comp with enough shields and damage. Shields benefit from two things that a champion has or can come with: 1 the runic affinity mastery that increases all heals and shields on you, and 2 your MR and Armour stats. A level 15 kog'mw with a level 13 janna gets shielded for an arbritray number, lets go with 300 shielded. After kog'maw's base armour, armour from 9 seals and janna's windspeakers, he now has 96 armour. Using the equation to calculate armour's mitigation 100/(100+96) and dividing 300 by that number we get the amount of ehp kog'maw is shielded for, 588.

My suggestion is that there should be an armour pen item that completely ignores armour for the parts of the hit that goes into the shield, so if kog has a 200 hp shield a flat hit for 300 will deal 200 to the shield then about 50hp damage to the kog'maw. The AP version could be 20% extra magic damage to shields or it could reduce mr for the shield portion to 0 then reduce mr further, maybe 25 mr or something like that. Only the buyer of these items get access to the shield breaker (maybe the armour pen component item could be a stylised sword breaker dagger, those things are cool) these items do not offer any armour/mr penetration beyond what's offered to shields.

Further consqeuences: (not necessarily downsides) windspeakers is less effective, but is still really good for protecting targets that have their shielding stripped, it's still a lot of armour given at that point. Maybe being hit by a shield breaker can prolong this part of windspeakers. Tanks get less use out of their shields, naut and sion with call of the colossus get hit less. I don't think it should be a last whisper item, adcs get enough armour pen and tanks should still be tanky to adcs. Assassins get more options to pull back into the game, they have a really hard time into shields, this item is not a good assassin item unless you need to deal with a medium amount of shielding. Being able to hit opponents who should be vulnerable should be important and if you stack enough shields you an still frontline a kog'maw into a dive comp or an assassin comp.

To conclude, I think the resistance stats given to shields should be hit, adcs should not have ready access to shieldbreaking, and a sword breaker dagger looks really cool you should look it up.